Foams have been used as sealing materials or buffer materials for electronic devices, including buffer materials for transportation, thermal insulating materials, packaging materials and building materials. In recent years, with miniaturization of electronic devices and an increase in size of screens, the area of the foams used as sealing materials or buffer materials decreases. It is therefore required for the foams to exhibit sufficient sealing ability or buffering ability even though they have a small area. In order to exhibit the sufficient ability despite the small area, methods for miniaturizing cells have been performed (Patent Documents 1 to 3).
However, in Patent Document 1 or 2 described above, the foam having uniform microcells are formed, but sufficient flexibility is not obtained because of its low expansion ratio. There is a possibility that this causes deterioration of buffering ability or screen unevenness of electronic devices. Further, sufficient flexibility may not be obtained, because the foamed structure is a closed cell structure. In Patent Document 3, the foam excellent in flexibility and having microcells is formed at a low discharge speed. However, when the discharge speed in producing the foam is high, the expansion ratio may be decreased, or the cells may become uneven. When the cells become uneven, the sealing ability or buffering ability may be deteriorated in the case where the foam having a small area is used.
That is to say, when the discharge speed is increased to produce the foam at a high production speed, no foam has been obtained at present, which has uniform microcells while maintaining a sufficient expansion ratio and flexibility, and does not lose sealing ability or buffering ability even in the case where the foam having a small area is used.
Patent Document 1: JP-A-2002-47326
Patent Document 2: Japanese Patent No. 4486941
Patent Document 3: JP-A-2010-270228